1. Field of the Invention
The present invention relates to locks and lock mechanisms for securing a door, usually of the pivoting type, to a door frame. More specifically, the present invention relates to a door locking apparatus which may easily be retro-fitted to an existing door, its associated lock mechanism and a door frame or fitted anew to increase the effort and time required to gain unauthorized entry past the door.
2. Description of the Prior Art
In the past, one of the easiest and most commonly used techniques to gain entry past a locked door having a bolt and its associated door frame was to forcibly separate the door and the door frame in the vicinity of the lock mechanism by, for example, a crow bar or similar type pry bar. Once separated, the lock mechanism's bolt no longer engages the door frame's bore and the door may be opened.
The military requires a secure door to prevent access to restricted areas. Compromising these areas to attempted break-ins by terrorist or other individuals trying to gain access could be disastrous to the military as well as the civilian population within the vicinity of the restricted area.
In the past, numerous attempts have been made to provide a door locking device which secures a door to its door frame. U.S. Pat. No. 1,280,993 to Issac Hammer, which issued Oct. 8, 1918 discloses a locking device comprising a striking portion having rectangular recesses therein with the recesses opening toward the door to which the lock is attached. The locking device also includes a striker plate, for attachment to the frame, which has a plurality of rectangular shackles extending from the striker plate to enter the recesses. The shackles also have perforations extending therethrough with the perforations being adapted to align with the recesses in the sides of the striking portion of the lock when the lock is closed on the striker plate. There are provided a plurality of bolts slidably mounted in the perforations for extension therethrough. There is also provided means for moving the bolts through the perforations and for withdrawing the same therefrom with the means embodying a rotary device having a thrust member operatively engaging the bolts.
A second example of a prior art device for securing a door to a door frame is disclosed in U.S. Pat. No. 5,406,814 to Micheal Zeager et al. which issued Apr. 18, 1995. This patent discloses a latch guarded door lock and frame system having a recessed surface which is provided in a hollow metal frame, and is dimensioned to accommodate a latch guard so that the external surfaces of the door, frame and latch guard are flush. The recessed surface of the frame behind the latch guard is further reinforced by employing a thicker wall than is used in the rest of the frame, and by welding a square metal tube into the recessed region. A medial metal support is also welded into the lock box cavity in order to prevent the lock box from collapsing under stress.
While these and similar door locking mechanisms of the past are generally satisfactory in private sector applications such as for use in a residence or a commercial business, the military has a need for door locking mechanism which will provide far greater security and which is relatively inexpensive to manufacture. More specifically, the military has a need for a door locking mechanism which is adapted for use with the dead bolt of commercially available dead bolt locks and which provides (1) resistance to door frame separation and (2) places the dead bolt into double shear. The military also has a need for a door locking mechanism which is completely resistant to forced entry for a time period of at least one minute.